Globoid cell leukodystrophy (GLD), also known as Krabbe disease, is a progressive and fatal neurodegenerative lysosomal storage disorder caused by the deficient activity of the hydrolytic enzyme ?- galactocerebrosidase (GALC), which is responsible for degrading the myelin lipids galactosylceramide (GalCer) and galactosylsphingosine (psychosine). In the absence of GALC, accumulation of psychosine, a known neurotoxin, causes loss of oligodendrocytes and subsequent widespread demyelination with patient death typically occurring in the second year of life. To date the only available therapeutic intervention for children is hematopoietic stem cell transplantation (HSCT) from donor umbilical cord blood or bone marrow. When employed early, HSCT has proven capable of slowing disease progression; however, the quality of life in children is poor due to neurologic deterioration resulting in loss of cognitive and motor functions. We hypothesize that genetically enhancing HSCs prior to transplantation will increase therapeutic levels of GALC, further attenuate disease progression, and prolong survival in GLD patients. To test this hypothesis, we will take advantage of a canine model of GLD that faithfully recapitulates the clinical disease progression, neuropathological alterations, and biochemical abnormalities observed in human patients. In Aim 1 we will optimize bone marrow harvest from young pups, HSC isolation, and lentiviral transduction in normal dogs utilizing a vector encoding GFP. In Aim 2 we will assess the safety and tolerability of lentiviral HSC gene therapy, including a novel preconditioning regimen, in normal dogs using an innovative lentiviral vector encoding canine GALC. In Aim 3 we will establish the efficacy of lentiviral HSC gene therapy in GLD dogs and compare to GLD dogs treated with HSCT alone (no lentiviral transduction) and untreated GLD controls. Safety and efficacy data from current clinical trials in other infantile-onset leukodystrophies and convincing preclinical data in our canine model of GLD could lead to rapid clinical implementation of lentiviral HSC gene therapy for Krabbe disease. Training specific to this disease model will occur through regular interactions with my sponsor, a board certified veterinary neurologist and NIH-funded investigator with extensive research experience utilizing large animal models to develop therapies for numerous LSD. This training will be augmented by 1) co-sponsorship with a viral vector specialist, and 2) collaboration with an expert in canine ex vivo gene therapy. The University of Pennsylvania provides adequate resources to complete the project and ample supplemental educational and training opportunities. The expertise of my selected sponsor and co-sponsor and resources of this institution will allow development of new skill sets and prepare me to become an independent investigator capable of translating therapies from the bench to use in patients.